In general, methotrexate is widely known to inhibit the metabolism of folic acid necessary for the synthesis of DNA in cells and the growth and division of cells. Specifically, methotrexate inhibits the enzymatic activity of dihydrofolate reductase (DHFR), which is one of the enzymes involved in folic acid metabolism. Thus, methotrexate is a drug applicable to various diseases by inhibiting cell proliferation, which is effective against autoimmune diseases, such as rheumatoid arthritis and psoriasis, and shows a very fast effect that alleviates the symptoms of the diseases within about 2 weeks after administration. However, methotrexate is difficult to use for a long period of time, because side effects that cause serious liver toxicity, gastrointestinal disorders and injuries of the kidneys and hematopoietic organs have been continuously reported. Also, it is formulated mainly for oral or injection administration, but the oral administration of methotrexate involves significant inconvenience, such as administering the active drug in a dosage of 2.5 mg at 12-hr intervals three times weekly. For this reason, there has been a continued need for the development of a novel method for drug delivery that can increase the drug delivery efficiency of methotrexate to reduce the dosage thereof so as to minimize the side effects and that can eliminate the inconvenience of injection and oral administration.
Meanwhile, PTD (protein transduction domain) is a low-molecular-weight peptide used for the penetration of a physiologically active molecule into host cells, and a first reported PTD is TAT found in the surface protein of the HIV virus in the year 1998. This TAT PTD was reported to effectively deliver large-size proteins having a molecular weight of more than 120 kDa into cells within a short time. Since then, several PTD proteins of different amino acid sequences having functions similar to TAT PTD have been found and research for novel drug development and DDS studies using these peptides has been suggested. Accordingly, leading countries in the medical and pharmaceutical fields have made many efforts to find novel PTD and develop novel drugs using the same. Also, the present inventors have performed studies to develop PTD, and as a result, developed novel PTD that shows a significantly higher effect than the prior reported PTDs in delivering macromolecules (e.g., proteins) into cells in vitro and in vivo (see PCT/KR2003/000121 and PCT/KR2003/000122).
Thus, the present inventors prepared a conjugate of PTD and methotrexate for the effective local delivery of methotrexate, and applied a novel pharmaceutical composition for transdermal delivery containing the conjugate on the skin and observed the results. As a result, we surprisingly found that methotrexate was delivered to lesion sites through the epidermis to show pharmacological effects, thereby completing the present invention.